Priority is claimed to Japanese Patent Application Serial Number 2001-346408, filed on Nov. 12, 2001 and Japanese Patent Application Serial Number 2002-020296, filed on Jan. 29, 2002, the disclosures of which are incorporated herein by reference in their entireties.
1. Field of the Invention
The preferred embodiments of present invention relate to, among other things, a lead frame and a resin sealing mold which improve the productivity and quality of a semiconductor device formed by resin sealing, and a method for manufacturing a semiconductor device using the same.
2. Description of the Related Art
The following description sets forth the inventors"" knowledge of related art and problems therein and should not be construed as an admission of knowledge in the prior art. Semiconductor devices have increased in capacity year after year. In accordance with this increase, the number of lead terminals that become various signal lines has tended to increase. In accordance with this tendency, a QFP (Quad Flat Package) type semiconductor device in which lead terminals extend outward from four directions has begun to be used. An example of this is disclosed in, for example, Japanese Unexamined Patent Publication No. H08-181160.
Hereinafter, background examples will be described with reference to the accompanying drawings. In this regard, FIG. 16 is a plan view of a lead frame, FIG. 17 is a perspective view of a mold, and FIG. 18 is a plan view of a lead frame after resin sealing.
A lead frame 1 shown in FIG. 16 can be formed by means of press-working or etching, and herein, six units are provided and semiconductor elements are mounted on the respective units. Each unit has a roughly square stage (island) 2 for mounting a semiconductor element and lead terminals extending in four directions outward around the stage 2. Furthermore, considering a mold, each unit has gates 4 as resin passages at the corners of a sealing region, and holes 5 for air vents when resin-sealing.
A mold 6 adapted to this lead frame 1 includes, as shown in FIG. 17, an upper mold 7 and a lower mold 8. The upper mold 7 and the lower mold 8 have a plurality of cavities 9 which face the stage 2 of the lead frame, pots 10 that are resin injection ports, and runners 11 which connect the cavities 9 and the pots 10 and serve as flow passages for filling the insides of the cavities 9 with a resin.
In this example, one pot 10 is provided for four cavities, and the runners 11 radially extend toward the respective cavities from the pots. The pots 10xe2x80x2 of the upper mold penetrate for injecting a resin from the upper side. Furthermore, cavities are also formed in the upper mold 7 although they are hidden in FIG. 17.
Next, a method for manufacturing a semiconductor device will be described. First, semiconductor elements are mounted on the stages 2 of the lead frame 1 shown in FIG. 16 via a silver paste that is an adhesive agent. The semiconductor element has a plurality of electrodes on the surface (not shown), and is mounted and fixed on the stage. Thereafter, the electrodes and lead terminals 3 are electrically connected by means of wire-bonding.
After thus mounting the semiconductor elements, the lead frame 1 is set between the upper mold 7 and the lower mold 8 shown in FIG. 17. Then, cavities as injection regions are formed by closing the molds.
Next, a resin to be melted is injected from the pots 10xe2x80x2 of the upper mold 7 at a predetermined pressure. The resin flows into the cavities of the upper mold 7 and the lower mold 7 and is filled in the cavities 9 via the runners 11. Then, the semiconductor elements are sealed. Before injecting the resin, air exists inside the cavities 9. However, at the stage of entry of the resin into the cavities, the resin presses the air and the air is released to, for example, air vents made in the upper mold 7. The air vents are formed as gaps that do not allow penetration of the resin.
After the resin is cooled and cured after being filled, the lead frame 1 is released by opening the molds. FIG. 18 shows the lead frame at this point. In this figure, for easy understanding of the resin flows, portions at which the pots and runners had existed when resin-sealing are shown by dashed lines. As clearly understood from FIG. 18, the resin flows in from the pot 10 that is positioned at the center of four sealing regions through the gates 4. Thereby, the semiconductor elements to be mounted on the stage and a part of the lead terminals 3 around the semiconductor elements are covered by the resin to form one package 12.
Subsequently, the connecting portions of the lead terminals 3 are cut, and the separated lead terminals 3 are bent, whereby a QFP type semiconductor device is completed.
As mentioned above, in the background method for manufacturing a semiconductor device, as shown in FIG. 17, air in the cavities 9 is led to the ends of the cavities 9 and then released to the outside from the cavities 9 through the air vents made in the mold. However, when the air is pressed out from the air vents, the resin forms burrs between the lead frame 1 and the upper mold 7 or between the lead frame 1 and the lower mold 8. The thickness of the resin burrs can be as thin as about 30 xcexcm. In some cases, when releasing the package 12 from the mold 6, the resin burrs are not released from the mold together with the package 12 and remain inside the mold. These remaining resin burrs can obstruct the paths for releasing the air inside the cavities during the next time of resin molding. As a result, the air cannot be released to the outside, and the air is compressed and remains inside the cavities 9. This is problematic because voids and unfilled regions are created in the package.
On the other hand, an air vent provided at the mold side has been considered. At a portion corresponding to the air vent, a part 13 of the lead frame exists, which is originally set so as not to be a lead terminal. On this part, resin burrs of about 30 xcexcm are created as in the above-mentioned case. In some cases, the burrs are left on the lead material during mold-release. In such cases, in the next process of lead bending, the resin burrs remaining on the lead frame 13 are crushed and remain on the bending mold. Since the burrs remain on the mold, in the next bending process this bending mold causes defects such as dents on the lead and lead deformation due to the crushed burrs.
In the case of a QFN (Quad Flat Non-leaded Package) type semiconductor device, the back surface can serve as a mounting surface, and the leads exposed to the back surface make electrical connection with a conductive pattern on a mounting substrate. However, in the background manufacturing method, resin burrs are created on at least the lead frame 13 including continuous packages. Therefore, when mounting the above-mentioned semiconductor device on the mounting substrate, mounting failures may occur due to resin burrs created at the package end.
There is a need in the art for improved systems and methods that overcome the above and/or other problems.
The various preferred embodiments of the present invention significantly improve upon existing systems and methods.
In some preferred embodiments, a lead frame can include, e.g.: at least one island; a pair of first connected line bodies and a pair of second connected line bodies which are disposed so as to surround the island; a plurality of leads extending from the first and second connected line bodies to the vicinity of the island; tie bars which integrate the leads and are disposed so as to surround the island; and air vent disposing regions formed in the vicinities of regions in which the first and second connected line bodies intersect; wherein at least in a first of the air vent disposing regions, a first air vent penetrating a lead forming region between the first air vent disposing region and the island and a second air vent that is formed independently in the vicinity of this first air vent are provided.
Furthermore, in the lead frame, preferably, the first air vent disposing region is formed integrally with two of the tie bars in the vicinity of an intersection of these two tie bars.
Furthermore, in some preferred embodiments, a resin sealing mold assembly can be provided having an upper mold and a lower mold which includes: a substantially hexahedral cavity for housing at least a lead frame and a semiconductor element; and at least one air releasing groove at contact surfaces of at least the upper mold or lower mold from at least one corner of the hexahedral cavity.
Furthermore, preferably, first air vents and second air vents that are independent from each other are formed in the lead frame to be pressed by the upper mold and the lower mold at a plurality of corners, and a resin injection gate is formed at least at one of the corners, one end of the resin injection gate positioned at a cavity side is formed at the contact surfaces proximate the cavity region, and the one end of the resin injection gate and the first air vent are continued to each other.
Furthermore, in some preferred embodiments, a method for manufacturing a semiconductor device can include: preparing a lead frame having at least tie bars for integrally supporting a plurality of leads and first air vents and second air vents, and on which semiconductor elements are mounted; housing the lead frame in a resin sealing mold that includes an upper mold and a lower mold and has a substantially hexahedral cavity and four corners of the hexahedron formed at a surface of contact between the upper mold and lower mold via the lead frame, and air releasing grooves at the contact surfaces of at least the upper mold or lower mold from a plurality of the corners; and leading air in the cavity through the first air vents, the air releasing grooves and the second air vents, and filling a resin in the cavity, whereby a resin sealed body is formed.
Furthermore, preferably, after releasing the lead frame from the mold, at least the resin in the first air vents remains in the first air vents, and in the tie bar cutting process, the first and second air vents are simultaneously eliminated.
First, in the lead frame of the preferred embodiments, first and second air vents can be formed independently from each other in an air vent forming region near the intersection of the first connected line body and the second connected line body. The lead frame can include that one end of the first air vent is continued to the cavity when resin-molding. Thereby, air existing in the cavity can reliably flow out to the outside of the cavity through the first air vent. As a result, substantially no air remains in the cavities and the resin can be filled in substantially the entire cavity, whereby a lead frame can be realized by which a package without unfilled regions can be formed.
Second, in the lead frame of the preferred embodiments, the first and second air vents can have a thickness almost equivalent to that of the lead frame. When resin-molding, air existing in the cavity is released, and at the same time, the resin also flows out. However, this resin can be securely contained inside the first and second air vents and the air releasing groove. Accordingly, the resin that has flown out can be cured and can become resin burrs outside the package. However, such resin burrs can be integrated with the lead frame via the first and second air vents and the air releasing groove. Accordingly, in a preferred semiconductor device manufacturing process, a lead frame can be realized which avoids disadvantages in which resin burrs are created and crushed to deteriorate the product quality or remain inside the mold during mold-release.
Third, the lead frame can include that the first and second air vents can be formed independently from each other, and the first air vent can be formed outward from the package forming region, and at the tip end side thereof, the second air vent can be formed. Thereby, the air existing in the cavity can be led to the outside of the package as much as possible. As a result, a lead frame can be realized in which, even when a connecting portion between the first air vent and the second air vent is closed by a resin, the air can be reliably released to the outside of the cavity.
Fourth, a resin sealing mold in some embodiments can include that an air releasing groove for connecting the first and second air vents formed in the above-mentioned lead frame can be formed at a position apart from the cavity end. This can avoid creation of thin resin burrs on the package outside surface. The resin cured in the air releasing groove can be handled integrally with the resin cured in the first and second air vents. Accordingly, when releasing the package from the mold, one can avoid having resin burrs crushed and remaining inside the mold, whereby a resin sealing mold can be realized which avoids deteriorating the product quality.
Fifth, the resin sealing mold can include that the tip end of a resin injection gate can be positioned at the contact surfaces of the upper mold and the lower mold apart from the cavity. Namely, also at the gate, a structure for injecting a resin by using the above-mentioned first air vent can be provided. Thereby, one can avoid having thin resin burrs created on the package outside surface. Accordingly, a resin sealing mold can be realized which suppresses mounting failures of, particularly, a leadless type semiconductor device.
Sixth, the semiconductor device manufacturing method can include that resin-molding is carried out by using the above-mentioned lead frame and resin sealing mold. Thereby, resin burrs outside the package and the lead frame can be integrally handled, so that the tie bar cutting process and the process of cutting the first and second air vent forming regions can be simultaneously carried out. Accordingly, at the point of the next lead bending process, all resin burrs outside the package can have been removed, dents or molding failures due to resin burrs crushed in the lead bending process can be inhibited from occurring in the leads.
Seventh, the semiconductor device manufacturing method can include that, as described in the fifth effect, the tie bar cutting process and the air vent cutting process can be simultaneously carried out. Thereby, the lead bending process that is a post-process can be continuously carried out. Accordingly, work time and capital investment can be reduced.
The above and/or other aspects, features and/or advantages of various embodiments will be further appreciated in view of the following description in conjunction with the accompanying figures. Various embodiments can include and/or exclude different aspects, features and/or advantages where applicable. In addition, various embodiments can combine one or more aspect or feature of other embodiments where applicable. The descriptions of aspects, features and/or advantages of particular embodiments should not be construed as limiting other embodiments or the claims